I've never been to this con, so I hope you don't mind my input, but I have to agree, that the location is absolutely disgusting, and is a safety hazard. And the fact they used the excuse that they wanted a creepy location is a total sack of crap. I'm not sure how running a con works, but I assume the people running it go to the location to check out the area, so for all we know, they knew the exact conditions, yet they still thought it was a good idea to set up the Vendor area there.
It sucks that the attendees and the artists/vendors had to go through that crap. And the fact that the person running the convention is being immature about it isn't helping the situation.